Page 239 - PC2019 Program & Proceedings

PLANT CANADA 2019

P51. Isoflavonoid metabolon and arogenate dehydratases in soybean (Glycine max): Identification
and Functional Characterization
*1
2
1
Sirjani, R. ; K. Pannunzio ; S. Kohalmi ; S. Dhaubhadel
1
1 The University of Western Ontario
2
Agriculture and Agri-Food Canada
Specialized metabolites in plants are imperative for a variety of stress response mechanisms.
Understanding the processes by which these metabolites are synthesized may help to improve the genetic
manipulation of crops. Previously we demonstrated the existence of an isoflavanoid metabolon in
soybean. Among many phenylpropanoid enzymes, two arogenate dehydratases (ADTs), necessary for the
synthesis of phenylalanine in plants, were shown to be part of the isoflavanoid metabolon. This was
surprising as the isoflavanoid metabolon is anchored to the endoplasmic reticulum, but GmADTs mostly
localize to the chloroplast. Phenylalanine is a precursor to many specialized metabolites, including
isoflavanoids. In other plants, some ADTs have been shown to possess prephenate dehydratase (PDT)
activity, which catalyzes an alternate route of phenylalanine synthesis. Soybean contains 9 putative
GmADTs, some of which may possess PDT activity. Here, we aim to functionally characterize all
GmADTs for their ADT/PDT activity. Six GmADTs were cloned into a yeast expression vector and
transformed into pha2, a knockout yeast strain that lacks PDT activity rendering the strain unable to
synthesize phenylalanine. PDT activity of GmADTs were determined by testing transformants for their
ability to complement pha2 on media without phenylalanine. Among the six GmADT isoforms,
GmADTU4 and GmADT12B were able to grow on media lacking phenylalanine, demonstrating their
ability to convert prephenate to phenylalanine. Characterization of other GmADTs for their PDT/ADT
activities is ongoing.

Ramtin Sirjani (rsirjani@uwo.ca)

P52. Photoacclimation to high-light in Chlamydomonas reinhardtii during senescence relies on
generating high-quenching centres at detached antenna
Meagher, E.; P. Rangsrikitphoti; B. Faridi; D. Durnford
UNB

Microalgae can respond to increases in light intensity by altering the concentration of photosynthetic
complexes. In exponential phase, the ability of Chlamydomonas reinhardtii to acclimate to excess light is,
in part, dependent on cell division to reduce the concentration of photosynthetic complexes. But, when
Chlamydomonas reinhardtii cells reach stationary phase, their ability to divide is limited. Our goal is to
dissect excess-light responses as cells approach stationary phase and to determine how the kinetics and
strategies of photoacclimation differ compared to cells in the exponential-growth phase. Cultures grown
to late exponential enter a declining growth phase, where cells continued a slow rate of growth for the
next seven days in both low (LL) and high-light (HL). Both cultures experience a conditional
senescence-related decline in chlorophyll levels, that is accelerated in HL. In HL, however, there is a
rapid decline in PSII reaction centers while the LHCII antenna remains stable. This was paralleled by a
rapid and sustained increase in Fo under HL that is absent under LL and only present in cells approaching
stationary phase. The antenna act as pH-dependent, quenching centres, presumably to protect the
senescing chloroplast against HL. Ultimately, the photoacclimation mechanism in senescing cultures is
distinct and shields the photosynthetic apparatus from excess light by long-term degradation of the PSII
reaction centres, changes that coincide with the induction of autophagy.

Dion Durnford (durnford@unb.ca)

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